Given what Zeta's done so far, and how nice it looks on IR, this might not be so far fetched as one would think. We are again seeing an eye-like feature on microwave., though it is considerably more defined in the northern half of the storm. At this rate, Energizer will start using the 2005 hurricane season in their ads - it keeps going and going and ....

Edit:
Ok, 10am NHC update is out, and they are also seeing this eye-like feature on microwave. They are also saying that conditions should be favorable for strengthening later today.

It looks like now that the shear is reducing, with the lopsided convection, it is starting to oscillate a bit. I don't know if it was tilted a bit from the SW shear, if the LLC is going to reform under the curved band of convection (I kind of doubt that) or it is just trying to get lined up vertically. Or maybe it is moving in response to that weak upper low Clark mentioned.

Anyway, now that it appears it is about to make it past that trough (which wasn't too certain last night) I was surprised that they kept the forecast to 55kts for the next 24-36 hours...maybe they're just waiting until this aft to see if the trough splits, before increasing the intensity forecast. We can assume because Zeta's a hybrid, slightly cooler water temps won't affect it too adversely, and with the lower shear, it's likely going to intensify. Right now I don't see any reason it couldn't make it to say 75-90kts for a short time, if it gets in the right spot. But I don't know so much, so maybe Clark or HF will post more reasons pro or con with regards to the extent of possible strengthening over the next day or so.

Edit--

The quikscat link is back. 1742 UTC showed Zeta not that strong at the surface, centered at just about 23N41W, which seems a little odd. Guess it really did oscillate around.

Zeta's convection is almost all sheared off. The southernmost part of the TC is close to an area of 40kt of shear, dropping off to around 20 kts just north of the center, coming from the WSW. Instead of enhancing the convection, shear from this direction pushed it away, possibly because this air was drier or coming from a different height (possibly higher?).

However it is very close to an area of low shear that is approaching. Now it would benefit Zeta to more a little further north, but it looks like since Zeta weakened it is being steered WSW by the lower level flow. We have seen hybrids can survive w/very little convection. Zeta should be sticking around until the lower shear moves closer, or it gets an opportunity to move further north, where it will be able to strengthen.

Since Zeta's convection was enhanced by shear yesterday, and destroyed by shear today, it is clear that height and direction (and perhaps humidity level) of the various levels of shear are critical to an intensity forecast.

Indeed, Lee!!!
FL is the abbreviation for my state of Florida.
I am trying to learn as well as understand what you people are saying when you use meteorlogical terms as I've had my fill of hurricanes in the 52 years I've been a Floridian.
Keeping it simple makes it much easier for me...lol.

SO...ALTHOUGH YOU'VE
HEARD THIS FROM US BEFORE...WE EXPECT A WEAKENING TREND TO COMMENCE
TOMORROW.
THEN...A GRADUAL TURN
TO THE RIGHT IS ANTICIPATED IN RESPONSE TO THE APPROACH OF A LARGE
LOW PRESSURE SYSTEM. IF ZETA WEAKENS FASTER THAN INDICATED
HERE...IT WOULD PROBABLY FOLLOW A MORE WESTWARD TRACK IN 3-4 DAYS.

My question...even though I speak english...is...is Zeta going north and then west or does all of this depend on weather or not Zeta weakens before all this?

ZETA IS A TENACIOUS CYCLONE AND BASED ON Dvorak CLASSIFICATIONS THE
WINDS ARE AT LEAST 55 KNOTS. THE CLOUD PATTERN IS IMPRESSIVE AND
CONSISTS OF AN AREA OF MODERATE CONVECTION NEAR THE CENTER AND A
CYCLONICALLY-CURVED CONVECTIVE BAND TO THE NORTHEAST. THE OUTFLOW
REMAINS ESTABLISHED AND THERE ARE NO SIGNS OF STRONG SHEAR. THE
GFDL INSISTS ON MAKING ZETA A HURRICANE AS AN UPPER-LEVEL SHARP
TROUGH APPROACHES. THIS COULD BE A CASE OF TROUGH INTERACTION
AIDING INTENSIFICATION. I WILL NOT BE SURPRISED IF THE GFDL
SOLUTION TURNS OUT TO BE CORRECT. IT HAS ALREADY BEAT ME A FEW
TIMES. HOWEVER...FOR THE SAKE OF CONTINUITY ONLY...THE INTENSITY
FORECAST KEEPS ZETA WITH 55 OR 50 KNOTS FOR THE NEXT 24 TO 36 HOURS
WITH A WEAKENING THEREAFTER.

Just walked in the door and just like I've done all season, made a beeline for the computer. The 10pm is out early.

Avila acknowledges Zeta is looking better, but once again the forecast is sticking with 55kts for "continuity." The latest quikscat pass missed both times, so this is reasonable. But in general I think battle fatigue must have set in. You can see on sat imagery that the shear has finally backed off, and as a result Zeta has strengthened enough to make some headway against what is left of the trough, which had been pretty stationary all day, and convection is occuring around the center. Some of the best-formed bands of convection in Zeta's lifetime (now wrapped half-way 'round) show both on sat and on the microwave pass from a couple hours ago.

Zeta is still moving between an area of strong shear to the south and less shear to the northwest. It doesn't appear that there will be any more n'ly component to the direction anytime soon (in fact if Zeta moves any further south they're going to have to readjust the floater image), so Zeta may not be able to take full advantage of the lower shear there, but regardless it seems there is another reason that Zeta will intensify:

Reviewing IR images from the last 24 hours it is clear the recent trough intensified Zeta. The discussion mentions this, but in the context of the oncoming trough, not the one that just passed:

...A CASE OF TROUGH INTERACTION AIDING INTENSIFICATION...

I'd be interested in hearing the basics of how this occurs (besides the fact that shear often does help develop convection). Does it have to be at a certain height or comparative direction? Because we saw today that the WSWly shear demolished the convection that had been built up by the shear from the trough earlier. What is unique about the shear assoc with a trough?

It appears that Zeta is about as interested in following the forecast points as TPC is in doing a specific intensity forecast. Zeta just slipped south of the first forecast point (it is doing trochoidal oscillations again, on a SW course).

What Lixion's getting at with the "trough interaction aiding intensification" -- hopefully in layman's terms -- is that if the trough is of the right size and distance from the storm, it can interact constructively with the storm, whether via enhanced outflow (more often an upper-low), superposition (almost always an upper trough and not a cutoff upper-low), or some other unknown technique. Usually, the narrower (in width/scale) of the trough, the more likely that it is going to match the width/scale of the tropical system and be able to enhance development. This most often is via baroclinic enhancement leading to an enhancement of the processes that lead to tropical development -- maybe I'll go into the nuts and bolts of it later in the winter, but I'm too drained this evening (anyone who watched the football game tonight will know why!), so my apologies. Generally accompanying this interaction is a reduction in the negative impacts of the trough, primarily shear. Elena from 1985 in the NE Gulf is the best-known case and there is a lot of research out in the field about that one...I'm pretty familiar with it, so if anyone has any further questions about this process, please feel free to ask!

These trough interactions generally tend to aid moderate tropical storms to weak hurricanes, allowing them to reach up to borderline category 2/3 intensity (although this high end isn't reached that often). The other type, briefly alluded to above, occurs when you get upper-lows distant from the storm that aid in enhancing outflow. We saw that several times this year -- Rita is the best case, but Katrina and Wilma had it too -- and is most often seen with major hurricanes, allowing them to reach higher intensities than they might otherwise. Generally accompanying these situations is a strong upper-ridge building over a very deep circulation, further enhancing the favorable environment. Such an environment is generally pretty resilient to change, leading to eyewall cycles being big.

Of course, Zeta here is a case of the former rather than the latter. Hope this helps clear it up a tad.

From 0645Z Satellite imagery. Zeta maintains...
The dry air intrusion appears to have weakened. As Zeta now has what would normally be a CDO. Symmetrical, and just slightly displaced from the main convection. It is centered over/ near the center of rotation. Northern channel of outflow is to the east toward the Azores Islands. Cirrus clouds are visible over the NW quadrant.
Lightning, while distant from the center, has dimished over the last few hours.

"...via baroclinic enhancement leading to an enhancement of the processes that lead to tropical development ..." Thanks much, Clark that is the key to what I was wondering. I knew it had to be baroclinic in nature yet result in convection of a tropical nature, but I had no idea how that could occur. It sounds very interesting and yes I want to hear more about that when you get an opportunity.

Beven's early morning discussion was thoughtfully detailed. The steering environment is clearly complex and changing from hour to hour, and there is a lack of data on the specifics of all the atmospheric features surrounding Zeta. Ironically as soon as he pegged the SW movement Zeta took off like a shot for the west. We know this is because of changes in the environment, but it is so much more fun to blame it on Zeta being deliberately perverse.

Zeta stayed in the area of high upper level shear all night (30 to 40 kts), but right on the border of a low shear environment at the mid level, so the convection shows little sign of shear. However, unexpectectly, once again the LLC is mostly exposed with just a small amount of convection to the NE, but we know Zeta can exist just fine with that small amount of convection. The LLC is beautifully defined, especially the center (look at the 1515Z vis sat image).

Convection has not built up again, so in the absence of strong shear at the mid level there are some other factors inhibiting the increase of intensity, perhaps water temperatures or the combination of winds at different levels around Zeta. But perhaps it is simply that in this kind of marginal environment major intensification is not possible unless there is a baroclinic element, and otherwise only a low level but nevertheless steady state of intensity can be maintained, until (inevitably) encountering strong shear which will completely remove the convection and finish the TC.

The 10am discussion mentions oncoming unfavorable winds which will weaken Zeta today. With such a small amount of convection left, and no obvious improvement in the environment forthcoming, it does look like the repeated forecast of gradual weakening is now becoming the case, unless we see a repeat of intensification for a short time as already occured from interaction with a trough.

There is always so much to learn from the TC that do not make it to hurricane status. This winter the ATL has provided an interesting laboratory to study (or to simply be puzzled) by one hybrid TC after another. The automatic adaptability of the hybrid TC to ensure its survival in the marginal changing environment, by taking on various combinations of subtropical and tropical presentations, is facinating.

Looking at the 5-day Java color movie of the high-level shear (CIMSS product), Zeta has for the most part, for the past three days, stayed just to the north of the tropical jet, and just right on the cusp of where the shear changes rapidly, from about 35 knots to 15 knots, with surprising consistency:

Coincidential in terms of it happening; significant in terms of it allowing the storm to stay alive. If trends at the end of that plot hold true for another couple of days, it could get caught in another one of those weak shear regions; then again, the weather doesn't always follow trends.

As Zeta moves into an area of greater shear at the high level almost all the convection is gone. The bare-bones LLC still has a lovely symmetry with a well-defined center, but it appears Zeta will continue to be steered into higher shear, and it isn't looking as though there is any way to recover the convection at this point.

The CIMSS product shows a level of favorable shear at mid-level, but shear can be seen on the sat visual acting on the shallow level of convection.

Even though Zeta has moved into an area of slightly warmer ocean temperatures the last 12 hours or so, apparently other conditions contribute to an environment that is not conducive to development.

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